High-Speed Downlink Packet Access (HSDPA) provides data transfer speeds and capacity in networks based on Universal Mobile Telecommunications System (UMTS). The use of Multiple-Input-Multiple-Output (MIMO) transmission schemes provide further gains when applied to HSDPA. MIMO-based transmissions involve the transmission of different data streams from different antennas or antenna elements.
For example, a MIMO-capable receiver would receive transmissions from the network from first and second transmit antennas (Tx1 and Tx2), including a Primary Common Pilot Channel (P-CPICH) signal from Tx1 and a Secondary Common Pilot Channel (S-CPICH) from Tx2. Pilot signals from the different antennas aid channel estimation at the MIMO receiver with respect to the involved Tx/Rx antenna pairings.
Of course, there may be legacy equipment not capable of operating in any MIMO modes, or equipment operating in channel conditions that do not support MIMO operation. Thus, it may be that all channels of interest for a non-MIMO receiver originated from Tx1, with the S-CPICH transmissions from Tx2 appearing as colored noise at the non-MIMO receiver. As will be appreciated by those of skill in the art, such noise is difficult to cancel using linear equalization.
Further, in the most general case, the non-MIMO receiver will not have any knowledge of whether S-CPICH transmissions are present, nor any knowledge of the particular channel or channels that carry S-CPICH transmissions. In this and in other regards, it therefore is difficult for non-MIMO receivers to deal with interference arising from S-CPICH transmissions in the same or surround areas of operation within the supporting network.